It is known that when a conjugated diene is polymerized in the presence of a polymerization catalyst, polymers having various microstructures can be obtained. A process for the preparation of a polybutadiene having a high cis-structure from a cobalt compound and an organic aluminum compound is known. A polybutadiene having a high cis-structure comprising 1,2-structure incorporated therein in a proper amount is expected to act as an impact modifier for vinyl aromatic polymer.
In recent years, the development of various olefins using a metallocene type complex as a catalyst has been actively under way. The polymerization of conjugated dienes has been studied as well.
Referring to the polymerization of conjugated dienes in the presence of metallocene type complex, a catalyst system made of cyclopentadienyl titanium trichloride (CpTiCl.sub.3) as a compound of transition metal of the group IV of the Periodic Table and methyl alumoxane is proposed in Macromol. Symp., vol. 89, p. 383 (1995), etc. However, the catalyst is disadvantageous in that it has a low polymerization activity.
JP-B-46-20494 (The term "JP-B" as used herein means an "examined Japanese patent publication") discloses a process for the preparation of a polybutadiene in the presence of a catalyst system made of CpVCl.sub.3 +(i-C.sub.4 H.sub.9).sub.3 Al/AlCl.sub.3 +H.sub.2 O. However, this catalyst system is disadvantageous in that it has a low polymerization activity.
A process for the preparation of a polybutadiene having a high cis-structure comprising 1,2-structure incorporated therein in a proportion of from 10 to 20% using a catalyst made of a vanadium (III) compound such as metallocene type complex of transition metal of the group V of the Periodic Table (e.g., CpVCl.sub.2.(PEt.sub.3).sub.2, Cp.sub.2 VCl) and methyl alumoxane is reported in Polymer, vol. 37 (2), p. 363 (1996).
Further, JP-A-9-202813 and JP-A-9-194526 (The term "JP-A" as used herein means an "unexamined published Japanese patent application") disclose a process for the preparation of a polybutadiene in the presence of a catalyst system made of a vanadium metallocene compound having a specific structure and an ionizing agent.
Moreover, EP 0778291A1 discloses a catalyst comprising:
(A) a compound of a transition metal of the group V of the Periodic Table represented by the following general formula: EQU R.sub.n M(O).sub.m X.sub.p.L.sub.a PA1 (B) at least one of (B1) an ionic compound comprising a non-coordinating anion and a cation and (B2) an aluminoxane, provided that said component (B) is an ionic compound comprising a non-coordinating anion and a cation (B1) when the combination of n, m, and p of said component (A) is (n=2, m=0, p=1) or (n=1, m=0, p=2). PA1 (i) Cyclopentadienyl vanadium trichloride PA1 (iia) 1,2-di-substituted cyclopentadienyl vanadium trichloride PA1 (iib) 1,3-di-substituted cyclopentadienyl vanadium trichloride PA1 (iii) 1,2,3-Tri-substituted cyclopentadienyl vanadium trichloride PA1 (iv) 1,2,4-Tri-substituted cyclopentadienyl vanadium trichloride PA1 (v) Tetra-substituted cyclopentadienyl vanadium trichloride PA1 (vi) Penta-substituted cyclopentadienyl vanadium trichloride PA1 (vii) Indenyl vanadium trichloride PA1 (viii) Substituted indenyl vanadium trichloride PA1 (ix) Monoalkoxide, dialkoxide and trialkoxide obtained by substituting chlorine atom in the compounds (i) to (viii) by alkoxy group PA1 (x) Methylated compound obtained by substituting chlorine atom in the compounds (i) to (ix) PA1 (xi) Compounds comprising R's connected to each other with hydrocarbon group or silyl group PA1 (xii) Dimethylated compounds obtained by substituting chlorine atom in the compounds (xi) by methyl group PA1 (xiii) Monoalkoxylated and dialkoxylated compounds obtained by substituting chlorine atom in the compounds (xi) by alkoxy group PA1 (xiv) Compounds obtained by substituting monochlorinated compounds (xiii) by methyl group PA1 (xv) Amidated compounds obtained by substituting chlorine atom in the compounds (i) to (viii) by amide group PA1 (xx) Methylated compounds obtained by substituting chlorine atom in the compounds (xv) by methyl group PA1 cyclopentadienyloxo vanadium dimethoxide, PA1 cyclopentadienyloxo vanadium di(iso-propoxide), PA1 cyclopentadienyloxo vanadium di(tert-butoxide), PA1 cyclopentadienyloxo vanadium diphenoxide, PA1 cyclopentadienyloxo vanadium methoxychloride, PA1 cyclopentadienyloxo vanadium iso-propoxychloride, PA1 cyclopentadienyloxo vanadium tert-butoxychloride, and PA1 cyclopentadienyloxo vanadium phenoxychloride. PA1 (cyclopentadienyl)(bisdiethylamide)oxo vanadium, PA1 (cyclopentadienyl)(bisdiiso-propylamide)oxo vanadium, and PA1 (cyclopentadienyl)(bisdi-n-octylamide)oxo vanadium.
wherein M represents a transition metal of the group V of the Periodic Table; R represents a cyclopentadienyl group, a substituted cyclopentadienyl group, an indenyl group, a substituted indenyl group, a fluorenyl group or a substituted fluorenyl group; O represents an oxygen atom; X represents a hydrogen atom, a halogen atom, a hydrocarbon group having 1 to 20 carbon atoms, an alkoxy group, an aryloxy group or an amido group; L represents a Lewis basic compound; n, m, and p each represent an integer selected to make a combination of (n=1, m=1, p=2), (n=1, m=0, p=3), (n=2, m=o, p=1) or (n=l, m=0, p=2); and a represents 0, 1 or 2, and
A polybutadiene has a so-called microstructure comprising a connection moiety produced by polymerization at the 1- and 4-positions (1,4-structure) and a connection moiety produced by polymerization at the 1- and 2-positions (1,2-structure) present in combination in its molecular chain. The 1,4-structures are classified into two types, i.e., cis-structure and trans-structure. On the other hand, the 1,2-structure comprises vinyl group as a side chain.
It is known that polybutadienes having different microstructures can be prepared depending on the kind of polymerization catalysts used. These polybutadienes are used for various purposes depending on their properties.
In particular, a polybutadiene having a microstructure comprising a high cis-structure having 1,2-structure incorporated therein in a proper amount and hence little trans-structure and a high molecular linearity has excellent properties such as high abrasion resistance, high heat generation resistance and high impact resilience.
JP-B-53-44188 discloses an impact-resistant polystyrene made of a polybutadiene having a 1,2-structural unit content of from 15 to 35%, a cis-1,4-structural unit content of from 20 to 85% and a 5% styrene solution viscosity (5% SV) of from 50 to 200 cps, provided that 5% styrene solution viscosity (5% SV) satisfies the relationship: 1.5ML.sub.1+4.ltoreq.5% styrene solution viscosity (5% SV).ltoreq.3ML.sub.1+4
In general, 5% SV and Tcp have the relationship 5% SV=Tcp.times.1.345. Accordingly, a formulation 1.12.ltoreq.Tcp/ML.sub.1+4.ltoreq.2.23 is given.